Although any micromechanical components are applicable, the present invention and its underlying object to be achieved are explained with reference to components which include inertial sensors based on silicon.
Micromechanical sensor devices for measuring acceleration, rotation rate, magnetic field, and pressure, for example, are generally known, and are mass-produced for various applications in the automotive and consumer sectors. In particular the miniaturization of components, functional integration, and effective cost reduction are trends in consumer electronics.
Nowadays, acceleration sensors and rotation rate sensors, as well as acceleration sensors and magnetic field sensors, are already manufactured as combination sensors (6d), and in addition there are first 9d modules, in which in each case 3-axis acceleration sensors, rotation rate sensors, and magnetic field sensors are combined into a single sensor device.
If, for example, small, inexpensive combinations of rotation rate sensors and acceleration sensors are to be manufactured, this may be carried out by providing a rotation rate sensor and an acceleration sensor on one chip. Both sensors may thus be produced on one substrate at the same time. The sensors are encapsulated on the substrate level via a cap wafer which provides two cavities per chip. In addition, different pressures may be set in the two cavities via an additional getter layer, so that each individual sensor has the optimal working pressure. A cost-effective product may be manufactured due to the fact that a very large number of sensors may be produced on one substrate at the same time.
To be able to install the sensor as a component on a circuit board, a sensor of this type together with an evaluation ASIC is glued to a carrier substrate, and contact is established between the sensor chip and the evaluation ASIC chip on the one hand and between the evaluation ASIC chip and the carrier substrate on the other hand. Solder balls are situated on the bottom side of the carrier substrate, with which the component is soldered and thus electrically connected to a circuit board. Lastly, the evaluation ASIC chip and the sensor chip are overmolded with a molding compound.
This method, in particular manufacturing the component from individual elements, is relatively complicated and expensive as a single process. In addition, the molding compound and the carrier substrate are required. Furthermore, only relatively large components may be manufactured.
In addition, manufacturing methods for rotation rate sensors and acceleration sensors which include an integrated CMOS evaluation circuit are known. For example, a structured oxide layer to which a monocrystalline functional layer 11 is bonded is provided on a CMOS wafer. An electrical connection between the functional layer and the CMOS evaluation circuit is established via a trenching process and filling with a conductive material. Via a further separation step, the functional layer is structured and self-supporting MEMS structures are produced, whose motion may then be easily capacitively excited or detected, for example. The functional layer is subsequently hermetically sealed with a cap wafer. Depending on the application, a suitable pressure is enclosed within the sealed volume. Contact areas for the CMOS wafer are exposed in order to relay the output signal of the ASIC chip via bonding wires and a suitable housing, as discusses in US 2010/0109102 A1, for example.
If very small sensors are to be manufactured, a housing may be dispensed with, and the combined ASIC-MEMS chip may be soldered directly to a circuit board, which is also referred to as a “bare die” system. However, to provide for direct solderability, the output signal of the ASIC chip must be led through the ASIC wafer to the rear side of the ASIC wafer through a via. A rewiring level is customarily provided there in order to then transmit the ASIC signal to the circuit board via solder balls, which are likewise provided on the rear side, as known from US 2012/0049299 A1, for example.
Via techniques in ASIC applications are expensive, and may generally be used only for very thin substrates. Thus far, via techniques for ASICs, due to other electrical requirements, have also not been developed as extensively as via techniques for capacitive MEMS signals. Consequently, the manufacturing costs as well as the failure rate in vias of ASICs are very high.
In addition, no ASIC circuit may be situated at locations where the vias are provided, resulting in additional surface area, and thus additional costs, for the ASIC chip. The self-supporting MEMS structures are anchored on the ASIC wafer. Since the ASIC wafer is very thin, and no intermediate substrate is present for stress decoupling, external stresses, for example mechanical stresses, may be caused by different coefficients of expansion of the circuit board and of the ASIC wafer, which easily bend the MEMS structures, which then results in error signals in the sensor.
In addition, these types of systems are difficult to test in comparison to discrete systems. In discrete systems, the discrete MEMS sensor as well as the evaluation ASIC may be tested before they are joined as a component. During an integration on the wafer level, it is possibly to test only the entire system, and also only after the vias of the ASIC have been provided. Therefore, the system is testable only at a very late stage, thus entailing numerous manufacturing risks. In addition, the testing depth is smaller, since some primary MEMS sensor parameters cannot be tested via the evaluation ASIC.